Mixed Polymer Superabsorbent Fibers And Method For Their Preparation

ABSTRACT

A method for making mixed polymer composite fibers in which a carboxyalkyl cellulose and a galactomannan polymer or a glucomannan polymer are blended in water to provide an aqueous solution; the aqueous solution treated with a first crosslinking agent to provide a gel; the gel is formed into get fibers using melt blowing, centrifugal spinning, wet spinning or dry-jet wet spinning; and the fibers treated with water miscible solvent to form mixed polymer composite fibers. The fiber has a diameter in the range of 50 μm to 1000 μm.

RELATIONSHIP TO OTHER APPLICATIONS

This application is a continuation-in-part of application Ser. No.11/537,849, Methods for the preparation of mixed polymer superabsorbentfibers, and application Ser. No. 11/537,989, Mixed polymersuperabsorbent fibers, both filed Oct. 2, 2006, and.

BACKGROUND OF THE INVENTION

Personal care absorbent products, such as infant diapers, adultincontinent pads, and feminine care products, typically contain anabsorbent core that includes superabsorbent polymer particlesdistributed within a fibrous matrix. Superabsorbents arewater-swellable, generally water-insoluble absorbent materials having ahigh absorbent capacity for body fluids. Superabsorbent polymers (SAPs)in common use are mostly derived from acrylic acid, which is itselfderived from petroleum oil, a non-renewable raw material. Acrylic acidpolymers and SAPs are generally recognized as not being biodegradable.Despite their wide use, some segments of the absorbent products marketare concerned about the use of non-renewable petroleum oil derivedmaterials and their non-biodegradable nature. Acrylic acid basedpolymers also comprise a meaningful portion of the cost structure ofdiapers and incontinent pads. Users of SAP are interested in lower costSAPs. The high cost derives in part from the cost structure for themanufacture of acrylic acid which, in turn, depends upon the fluctuatingprice of petroleum oil. Also, when diapers are discarded after use theynormally contain considerably less than their maximum or theoreticalcontent of body fluids. In other words, in terms of their fluid holdingcapacity, they are “over-designed”. This “over-design” constitutes aninefficiency in the use of SAP. The inefficiency results in part fromthe fact that SAPs are designed to have high gel strength (asdemonstrated by high absorbency under load or AUL). The high gelstrength (upon swelling) of currently used SAP particles helps them toretain a lot of void space between particles, which is helpful for rapidfluid uptake. However, this high “void volume” simultaneously results inthere being a lot of interstitial (between particle) liquid in theproduct in the saturated state. When there is a lot of interstitialliquid the “rewet” value or “wet feeling” of an absorbent product iscompromised.

In personal care absorbent products, U.S. southern pine fluff pulp iscommonly used in conjunction with the SAP. This fluff is recognizedworldwide as the preferred fiber for absorbent products. The preferenceis based on the fluff pulp's advantageous high fiber length (about 2.8mm) and its relative ease of processing from a wetland pulp sheet to anairlaid web. Fluff pulp is also made from renewable and biodegradablecellulose pulp fibers. Compared to SAP, these fibers are inexpensive ona per mass basis, but tend to be more expensive on a per unit of liquidheld basis. These fluff pulp fibers mostly absorb within the intersticesbetween fibers. For this reason, a fibrous matrix readily releasesacquired liquid on application of pressure. The tendency to releaseacquired liquid can result in significant skin wetness during use of anabsorbent product that includes a core formed exclusively fromcellulosic fibers. Such products also tend to leak acquired liquidbecause liquid is not effectively retained in such a fibrous absorbentcore.

Superabsorbent produced in fiber form has a distinct advantage overparticle forms in some applications. Such superabsorbent fiber can bemade into a pad form without added non superabsorbent fiber. Such padswill also be less bulky due to elimination or reduction of the nonsuperabsorbent fiber used. Liquid acquisition will be more uniformcompared to a fiber pad with shifting superabsorbent particles.

A need therefore exists for a fibrous superabsorbent material that issimultaneously made from a biodegradable renewable resource likecellulose that is inexpensive. In this way, the superabsorbent materialcan be used in absorbent product designs that are efficient. These andother objectives are accomplished by the invention set forth below.

SUMMARY OF THE INVENTION

The present invention provides a method for making mixed polymercomposite fibers. In the method, a carboxyalkyl cellulose and agalactomannan polymer or glucomannan polymer are blended in water toprovide an aqueous solution; the aqueous solution treated with a firstcrosslinking agent to provide a gel.

In one embodiment the get is then spun into gel fibers using centrifugalspinning. In another embodiment the gel is extruded into gel fibersusing meltblowing. In another embodiment the gel is formed into gelfibers using wet spinning.

In an embodiment the spun or extruded gel fibers are precipitated intosolid fibers by being passed into a solvent bath to provide mixedpolymer composite fibers. In another embodiment the spun or extruded gelfibers are precipitated into solid fibers by being sprayed with asolvent to provide mixed polymer composite fibers. The solvent bath orspray uses a water miscible solvent.

In another embodiment the bath or spray may contain a secondcrosslinking agent to provide further crosslinking of the fibers.

The mixed polymer composite fibers may then be dried.

The method allows fibers of a specific and predetermined diameter andcross-section to be formed. The fibers may have diameter of 50 μm to1000 μm. In some instances the diameter of the fibers may vary along thefiber length.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a dry-jet wet process.

FIG. 2 is a diagram of a centrifugal spinning process.

FIG. 3 is a diagram of a meltblow spinning process.

FIG. 4 is a diagram of a meltblow head for the meltblow spinningprocess.

FIG. 5 is a diagram of a wet spinning process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for making mixed polymercomposite fibers. In the method, a carboxyalkyl cellulose and agalactomannan polymer or glucomannan polymer are blended in water toprovide an aqueous solution; the aqueous solution treated with a firstcrosslinking agent to provide a gel; the gel is then spun or extrudedinto fibers using centrifuge spinning, meltblowing or wet spinningmethods. The spun or extruded fibers pass into a solvent bath to provideformed fibers. The solvent is a water-miscible solvent/water mixture.The bath may contain a second crosslinking agent to provide furthercrosslinking of the fibers.

The mixed polymer composite fiber is a fiber comprising a carboxyalkylcellulose and a galactomannan polymer or glucomannan polymer. Thecarboxyalkyl cellulose, which is mainly in the sodium salt form, can bein other salts forms such as potassium and ammonium forms. The mixedpolymer composite fiber is formed by intermolecular crosslinking ofmixed polymer molecules, and is water insoluble and water-swellable.

As used herein, the term “mixed polymer composite fiber” refers to afiber that is the composite of two different water soluble polymers(i.e., mixed polymers). The mixed polymer composite fiber is ahomogeneous composition that includes two associated polymers: (1) acarboxyalkyl cellulose and (2) either a galactomannan polymer or aglucomannan polymer.

The carboxyalkyl cellulose useful in making the mixed polymer compositefiber has a degree of carboxyl group substitution (DS) of from about 0.3to about 2.5. In one embodiment, the carboxyalkyl cellulose has a degreeof carboxyl group substitution of from about 0.5 to about 1.5.

Although a variety of carboxyalkyl celluloses are suitable for use inmaking the mixed polymer composite fiber, in one embodiment, thecarboxyalkyl cellulose is carboxymethyl cellulose. In anotherembodiment, the carboxyalkyl cellulose is carboxyethyl cellulose.

The carboxyalkyl cellulose is present in the mixed polymer compositefiber in an amount from about 60 to about 99% by weight based on theweight of the mixed polymer composite fiber. In one embodiment, thecarboxyalkyl cellulose is present in an amount from about 80 to about95% by weight based on the weight of the mixed polymer composite fiber.In addition to carboxyalkyl cellulose derived from wood pulp containingsome carboxyalkyl hemicellulose, carboxyalkyl cellulose derived fromnon-wood pulp, such as cotton linters, is suitable for preparing themixed polymer composite fiber. For carboxyalkyl cellulose derived fromwood products, the mixed polymer fibers include carboxyalkylhemicellulose in an amount up to about 20% by weight based on the weightof the mixed polymer composite fiber.

The galactomannan polymer useful in making the mixed polymer compositefiber can include any one of a variety of galactomannan polymers. In oneembodiment, the galactomannan polymer is guar gum. In anotherembodiment, the galactomannan polymer is locust bean gum. In a furtherembodiment, the galactomannan polymer is tar gum. In another embodiment,the galactomannan polymer is fenugreek gum.

The glucomannan polymer useful in making the mixed polymer compositefiber can include any one of a variety of glucomannan polymers. In oneembodiment, the glucomannan polymer is konjac gum.

The galactomannan polymer or glucomannan polymer is present in an amountfrom about 1 to about 20% by weight based on the weight of the mixedpolymer composite fiber. In one embodiment, the galactomannan polymer orglucomannan polymer is present in an amount from about 1 to about 15% byweight based on the weight of the mixed polymer composite fiber. In afurther embodiment, the galactomannan polymer or glucomannan polymer ispresent in an amount from about 2 to about 15% by weight based on theweight of the mixed polymer composite fiber.

The preparation of the mixed polymer composite fiber is a multistepprocess. First, the water-soluble carboxyalkyl cellulose andgalactomannan polymer or glucomannan polymer are dissolved in water.Then, a first crosslinking agent is added and mixed to obtain a mixedpolymer composite gel formed by intermolecular crosslinking ofwater-soluble polymers.

Suitable first crosslinking agents include crosslinking agents that arereactive towards hydroxyl groups and carboxyl groups. Representativecrosslinking agents include metallic crosslinking agents, such asaluminum (III) compounds, titanium (IV) compounds, bismuth (III)compounds, boron (III) compounds, and zirconium (IV) compounds. Thenumerals in parentheses in the preceding list of metallic crosslinkingagents refers to the valency of the metal.

In one embodiment the gel is formed into fibers through the use of adry-jet wet spinning process. A diagram of the dry jet wet spinningprocess is shown in FIG. 1. The gel is pumped through a transfer line 1through a spinning block 2, through the orifices of spinneret 3 througha layer of gas or air 5 and into a bath 6 where the fibers 4 areconducted by guides 7 and 8 and precipitated into mixed polymercomposite fiber 15 which is wound up on a take-up roll 9.

In another embodiment the gel is formed into fibers through the use ofcentrifugal spinning. FIG. 2 is a diagram of centrifugal spinning. Incentrifugal spinning the gel 20 is directed in a generally hollowcylinder or drum 21 with a closed base and a multiplicity of smallapertures 22 in its sidewalls 23. As the cylinder rotates, the gel isforced out horizontally through the apertures as thin gel strands or gelfibers 24. As the strands meet resistance from the surrounding air theyare drawn or stretched. The amount of stretch will depend on readilycontrollable factors such as cylinder rotational speed, orifice size ofthe apertures and the viscosity of the gel. The strands either fall bygravity or are forced down by air flow into a water miscible solvent 25held in a basin 26 where the gel fibers are precipitated into mixedpolymer composite fibers. Alternatively, the fibers 24 may be sprayedwith a water-miscible solvent from a ring of spray nozzles 27 fed byline 28.

In another embodiment the gel is formed into fibers through the use ofmelt blowing technology. FIGS. 3 and 4 are diagrams of melt blowing. Inmelt blowing the gel is directed to an extruder 32 which forces the gelthrough an orifice head 34 having a multiplicity of orifices 36. Air oranother gas is supplied through lines 38 and surrounds and transportsextruded gel fibers 40. The air or gas moves in parallel with the fibersand impinges on the fibers, transporting the fibers, and drawing andstretching the fibers. The gel fibers move into the bath 42 whichcontains a water-miscible solvent 44 which precipitates the gel fibersto form mixed polymer composite fibers. As in centrifugal spinning thegel fibers may be sprayed with the water-miscible solvent to form themixed polymer composite fibers instead of being placed in a bath. Beloworifice 36 and above bath 42, solvent circulated from bath 42 can besprayed onto fibers 40 too.

FIG. 4 shows a typical extrusion orifice. The orifice plate 50 is boredwith a multiplicity of orifices 36. The plate 50 is held to the body ofthe extrusion head 51 by a series of cap screws 52. An internal member53 forms the extrusion ports 54 for the gel. It is embraced by airpassages 55 that surround the extruded gel fibers 40 causing them to bedrawn and to assist in their transport to the bath. The amount the gelfibers are drawn or stretched will depend on the viscosity of the gel,the speed of the fiber travel and the gas travel, and the angle betweenthe gas and the fiber. Depending on the speed and angle of the fiber andgas, long continuous fibers may be formed or short fibers may be formed.

In another embodiment the gel may be formed into fibers by wet spinning.A diagram of wet spinning is shown in FIG. 5. In wet spinning the gel ispassed by a pump 60 through pipe 61 leading into bath 62 containing thewater-miscible solvent 63. The gel is extruded through spinneret 64directly into the bath to form mixed polymer composite fibers 65 whichare guided from by the transfer roll 66 to a take up roll. The amount oftime of the gel in the bath will depend on the speed of the fibers andthe placement of the spinneret in the bath. A short retention time isshown. A different placement of the spinneret will increase theretention time in the bath. The fibers are fixed in the bath.Alternatively, fiber 65 can be collected on a moving screen.

The mixed polymer composite fiber thus obtained may be furthercrosslinked (e.g., surface crosslinked) by treating with a secondcrosslinking agent in the treating bath or spray. The secondcrosslinking agent can be the same as or different from the firstcrosslinking agent. The need for a second crosslinking step will dependon the amount of crosslinking that has been generated in the initialcrosslinking. If the initial crosslinking is light then the fibergenerated after first crosslinking has a high level of sliminess whenhydrated and forms soft gels and cannot be used in absorbentapplications without further treatment. If the crosslinking in the firstor initial crosslinking is greater the fiber generated after the firstcrosslinking will not be slimy and will be a hard gel.

The mixed polymer fibers are substantially insoluble in water whilebeing capable of absorbing water. The fibers are rendered waterinsoluble by virtue of a plurality of non-permanent intra-fiber metalcrosslinks. As used herein, the term “non-permanent intra-fiber metalcrosslinks” refers to the nature of the crosslinking that occurs withinindividual modified fiber (i.e., intra-fiber) and among and between eachfiber's constituent polymer molecules.

The fibers are intra-fiber crosslinked with metal crosslinks. The metalcrosslinks arise as a consequence of an associative interaction (e.g.,bonding) between functional groups (e.g., carboxy, carboxylate, orhydroxyl groups) of the fiber's polymers and a multi-valent metalspecies. Suitable multi-valent metal species include metal ions having avalency of three or greater and that are capable of forming associativeinterpolymer interactions with functional groups of the polymermolecules (e.g., reactive toward associative interaction with thecarboxy, carboxylate, or hydroxyl groups). The polymers are crosslinkedwhen the multi-valent metal species form associative interpolymerinteractions with functional groups on the polymers. A crosslink may beformed intramolecularly within a polymer or may be formedintermolecularly between two or more polymer molecules within a fiber.The extent of intermolecular crosslinking affects the water solubilityof the composite fibers (i.e., the greater the crosslinking, the greaterthe insolubility) and the ability of the fiber to swell on contact withan aqueous liquid.

The fibers include non-permanent intrafiber metal crosslinks formed bothintermolecularly and intramolecularly in the population of polymermolecules. As used herein, the term “non-permanent crosslink” refers tothe metal crosslink formed with two or more functional groups of apolymer molecule (intramolecularly) or formed with two or morefunctional groups of two or more polymer molecules (intermolecularly).It will be appreciated that the process of dissociating andre-associating (breaking and reforming crosslinks) the multi-valentmetal ion and polymer molecules is dynamic and also occurs during liquidacquisition. During water acquisition the individual fibers and fiberbundles swell and change to gel state. The ability of non-permanentmetal crosslinks to dissociate and associate under water acquisitionimparts greater freedom to the gels to expand than if the gel wasrestrictively crosslinked by permanent crosslinks that do not have theability to dissociate and re-associate. Covalent organic crosslinks,such as ether crosslinks, are permanent crosslinks that do notdissociate and re-associate.

The fibers have fiber widths of from about 2 μm to about 100 μm andcoarseness that varies from soft to rough. Melt blown fibers havediameters that vary along the length of the fiber to give an undulatingcross section to the fiber.

The fibers are highly absorptive fibers. The fibers can have a FreeSwell Capacity of from about 25 to about 60 g/g (0.9% saline solution),a Centrifuge Retention Capacity (CRC) of from about 15 to about 35 g/g(0.9% saline solution), and an Absorbency Under Load (AUL) of from about15 to about 30 g/g (0.9% saline solution).

The fibers can be formed into pads by conventional methods includingair-laying techniques to provide fibrous pads having a variety of liquidwicking characteristics. For example, pads can absorb liquid at a rateof from about 10 ml/sec to about 0.005 ml/sec (0.9% saline solution/10ml application). The integrity of the pads can be varied from soft tovery strong.

The mixed polymer composite fibers are water insoluble and waterswellable. Water insolubility is imparted to the fiber by intermolecularcrosslinking of the mixed polymer molecules, and water swellability isimparted to the fiber by the presence of carboxylate anions withassociated cations. The fibers are characterized as having a relativelyhigh liquid absorbent capacity for water (e.g., pure water or aqueoussolutions, such as salt solutions or biological solutions such asurine). Furthermore, because the mixed polymer fiber has the structureof a fiber, the mixed polymer composite fiber also possesses the abilityto wick liquids. The mixed polymer composite fiber advantageously hasdual properties of high liquid absorbent capacity and liquid wickingcapacity.

Mixed polymer fibers having slow wicking ability of fluids are useful inmedical applications, such as wound dressings and others. Mixed polymerfibers having rapid wicking capacity for urine are useful in personalcare absorbent product applications. The mixed polymer fibers can beprepared having a range of wicking properties from slow to rapid forwater and 0.9% aqueous saline solutions.

The mixed polymer composite fibers are useful as superabsorbents inpersonal care absorbent products (e.g., infant diapers, feminine careproducts and adult incontinence products). Because of their ability towick liquids and to absorb liquids, the mixed polymer composite fibersare useful in a variety of other applications, including, for example,wound dressings, cable wrap, absorbent sheets or bags, and packagingmaterials.

In one aspect of the invention, methods for making mixed polymercomposite fibers are provided. In the methods, the mixed polymercomposite fibers are formed by spinning or extruding the gel into afiber and then precipitating the fiber to form a mixed polymer compositefiber by a water-miscible solvent bath or spray.

In one embodiment, the method for making the mixed polymer compositefibers (crosslinked fibers) includes the steps of: (a) blending acarboxyalkyl cellulose (e.g., mainly salt form) and a galactomannanpolymer or a glucomannan polymer in water to provide an aqueoussolution; (b) treating the aqueous solution with a first crosslinkingagent to provide a gel; (c) forming a fiber from the gel by centrifugalspinning; and (d) treating the gel fiber in a water-miscible solventbath or by water-miscible solvent spray to provide to precipitate themixed polymer composite fibers.

In another embodiment, the method for making the mixed polymer compositefibers (crosslinked fibers) includes the steps of: (a) blending acarboxyalkyl cellulose (e.g., mainly salt form) and a galactomannanpolymer or a glucomannan polymer in water to provide an aqueoussolution; (b) treating the aqueous solution with a first crosslinkingagent to provide a gel; (c) forming a fiber from the gel by meltblowing; and (d) treating the gel fiber in a water-miscible solvent bathor by water-miscible solvent spray to provide mixed polymer compositefibers.

In another embodiment, the method for making the mixed polymer compositefibers (crosslinked fibers) includes the steps of: (a) blending acarboxyalkyl cellulose (e.g., mainly salt form) and a galactomannanpolymer or a glucomannan polymer in water to provide an aqueoussolution; (b) treating the aqueous solution with a first crosslinkingagent to provide a gel; (c) forming a fiber from the gel by wetspinning; and (d) treating the gel fiber in a water-miscible solventbath to provide mixed polymer composite fibers.

In another embodiment, the method for making the mixed polymer compositefibers (crosslinked fibers) includes the steps of: (a) blending acarboxyalkyl cellulose (e.g., mainly salt form) and a galactomannanpolymer or a glucomannan polymer in water to provide an aqueoussolution; (b) treating the aqueous solution with a first crosslinkingagent to provide a gel; (c) forming a fiber from the gel by jet-dry wetspinning; and (d) treating the gel fiber in a water-miscible solventbath to provide mixed polymer composite fibers.

In another embodiment step (d) in each of the above methods may includetreating the fibers with a second crosslinking agent (e.g., surfacecrosslinking) by having the second crosslinking agent in the bath orspray to provide mixed polymer composite fibers.

The fibers may have a diameter of 50 μm to 1000 μm. Melt blown fibersmay be nonuniform in diameter along the fiber length.

The mixed polymer composite fibers so prepared can be dried.

The fibers may have a diameter of 50 μm to 1000 μm.

In the process, a carboxyalkyl cellulose and a galactomannan polymer ora glucomannan polymer are blended in water to provide an aqueoussolution.

Suitable carboxyalkyl celluloses have a degree of carboxyl groupsubstitution of from about 0.3 to about 2.5, and in one embodiment havea degree of carboxyl group substitution of from about 0.5 to about 1.5.In one embodiment, the carboxyalkyl cellulose is carboxymethylcellulose. The aqueous solution includes from about 60 to about 99% byweight carboxyalkyl cellulose based on the weight of the product mixedpolymer composite fiber. In one embodiment, the aqueous solutionincludes from about 80 to about 95% by weight carboxyalkyl cellulosebased on the weight of mixed polymer composite fiber.

Suitable galactomannan polymers include guar gum, locust bean gum, taragum, and fenugreek gum. Suitable glucomannan polymers include konjacgum. The galactomannan polymer or glucomannan polymer can be fromnatural sources or obtained from genetically-modified plants. Theaqueous solution includes from about 1 to about 20% by weightgalactomannan polymer or glucomannan polymer based on the weight of themixed polymer composite fibers, and in one embodiment, the aqueoussolution includes from about 1 to about 15% by weight galactomannanpolymer or glucomannan polymer based on the weight of mixed polymercomposite fibers.

In the method, the aqueous solution including the carboxyalkyl celluloseand galactomannan polymer or glucomannan polymer is treated with asuitable amount of a first crosslinking agent to provide a gel.

Suitable first crosslinking agents include crosslinking agents that arereactive towards hydroxyl groups and carboxyl groups. Representativecrosslinking agents include metallic crosslinking agents, such asaluminum (II) compounds, titanium (IV) compounds, bismuth (III)compounds, boron (III) compounds, and zirconium (IV) compounds. Thenumerals in parentheses in the preceding list of metallic crosslinkingagents refers to the valency of the metal.

Representative metallic crosslinking agents include aluminum sulfate;aluminum hydroxide; dihydroxy aluminum acetate (stabilized with boricacid); other aluminum salts of carboxylic acids and inorganic acids;other aluminum complexes, such as Ultrion 8186 from Nalco Company(aluminum chloride hydroxide); boric acid; sodium metaborate; ammoniumzirconium carbonate; zirconium compounds containing inorganic ions ororganic ions or neutral ligands; bismuth ammonium citrate; other bismuthsalts of carboxylic acids and inorganic acids; titanium (IV) compounds,such as titanium (IV) bis(triethylaminato) bis(isopropoxide)(commercially available from the Dupont Company under the designationTyzor TE); and other titanates with alkoxide or carboxylate ligands.

The first crosslinking agent is effective for associating andcrosslinking the carboxyalkyl cellulose (with or without carboxyalkylhemicellulose) and galactomannan polymer molecules. The firstcrosslinking agent is applied in an amount of from about 0.1 to about20% by weight based on the total weight of the mixed polymer compositefiber. The amount of first crosslinking agent applied to the polymerswill vary depending on the crosslinking agent. In general, the fibershave an aluminum content of about 0.04 to about 0.8% by weight based onthe weight of the mixed polymer composite fiber for aluminum crosslinkedfibers, a titanium content of about 0.10 to about 1.5% by weight basedon the weight of the mixed polymer composite fiber for titaniumcrosslinked fibers, a zirconium content of about 0.09 to about 2.0% byweight based on the weight of the mixed polymer composite fiber forzirconium crosslinked fibers, and a bismuth content of about 0.90 toabout 5.0% by weight based on the weight of the mixed polymer compositefiber for bismuth crosslinked fibers.

The gel formed by treating the aqueous solution of a carboxyalkylcellulose and a galactomannan polymer with a first crosslinking agent isthen spun or extruded into a gel fiber by centrifugal spinning,meltblowing or wet spinning.

The spun or extruded gel fibers are then precipitated to form mixedpolymer composite fibers by treatment by a water-miscible solvent ineither a bath or spray.

Suitable water-miscible solvents include water-miscible alcohols andketones. Representative water-miscible solvents include acetone,methanol, ethanol, isopropanol, and mixtures thereof. In one embodiment,the water-miscible solvent is ethanol. In another embodiment, thewater-miscible solvent is isopropanol.

If the fibers formed from the spinning or extrusion step are treated ina mixture of water and a water miscible solvent, the proportions ofwater and solvent must be such that the fibers do not lose their fiberform and form a gel.

A second crosslinking agent may be used in the bath or spray. The secondcrosslinking agent is effective in further crosslinking (e.g., surfacecrosslinking) the mixed polymer composite fibers. Suitable secondcrosslinking agents include crosslinking agents that are reactivetowards hydroxyl groups and carboxyl groups. The second crosslinkingagent can be the same as or different from the first crosslinking agent.Representative second crosslinking agents include the metalliccrosslinking agents noted above useful as the first crosslinking agents.

The second crosslinking agent can be applied at a relatively higherlevel than the first crosslinking agent per unit mass of fiber. Thisprovides a higher degree of crosslinking on the surface of the fiberrelative to the interior of the fiber. As described above, metalcrosslinking agents form crosslinks between carboxylate anions and metalatoms or hydroxyl oxygen and metal atoms. These crosslinks can migratefrom one oxygen atom to another when the mixed polymer fiber absorbswater and forms a gel. However, having a higher level of crosslinks onthe surface of the fiber relative to the interior provides asuperabsorbent fiber with a suitable balance in free swell, centrifugeretention capacity, absorbency under load for aqueous solutions andlowers the gel blocking that inhibits liquid transport.

The second crosslinking agent is applied in an amount from about 0.1 toabout 20% by weight based on the total weight of mixed polymer compositefibers. The amount of second crosslinking agent applied to the polymerswill vary depending on the crosslinking agent. The product fibers havean aluminum content of about 0.04 to about 2.0% by weight based on theweight of the mixed polymer composite fiber for aluminum crosslinkedfibers, a titanium content of about 1.0 to about 4.5% by weight based onthe weight of the mixed polymer composite fiber for titanium crosslinkedfibers, a zirconium content of about 0.09 to about 6.0% by weight basedon the weight of the mixed polymer composite fiber for zirconiumcrosslinked fibers; and a bismuth content of about 0.09 to about 5.0% byweight based on the weight of the mixed polymer composite fiber forbismuth crosslinked fibers.

The second crosslinking agent may be the same as or different from thefirst crosslinking agent. Mixtures of two or more crosslinking agents indifferent ratios may be used in each crosslinking step.

The resultant fibers, either with one crosslinking agent or surfacecrosslinked with a second crosslinking agent, are then washed with awater-miscible solvent and air dried or oven dried below 80° C. toprovide the mixed polymer composite fibers.

The preparation of representative mixed polymer composite fibers aredescribed in Examples 1-2.

Test Methods Free Swell and Centrifuge Retention Capacities

The materials, procedure, and calculations to determine free swellcapacity (g/g) and centrifuge retention capacity (CRC) (gig) were asfollows.

Test Materials:

Japanese pre-made empty tea bags (available from Drugstore.com, INPURSUIT OF TEA polyester tea bags 93 mm×70 mm with fold-over flap.(http:www.mesh.ne.jp/tokiwa/)).

Balance (4 decimal place accuracy, 0.0001 g for air-dried superabsorbentpolymer (ADS SAP) and tea bag weights); timer; 1% saline; drip rack withclips (NLM 211); and lab centrifuge (NLM 211, Spin-X spin extractor,model 776S, 3,300 RPM, 120 v).

Test Procedure:

1. Determine solids content of ADS.

2. Pre-weigh tea bags to nearest 0.0001 g and record.

3. Accurately weigh 0.2025 g±0.0025 g of test material (SAP), record andplace into pre-weighed tea bag (air-dried (AD) bag weight). (ADSweight+AD bag weight=total dry weight).

4. Fold tea bag edge over closing bag.

5. Fill a container (at least 3 inches deep) with at least 2 inches with1% saline.

6. Hold tea bag (with test sample) flat and shake to distribute testmaterial evenly through bag.

7. Lay tea bag onto surface of saline and start timer.

8. Soak bags for specified time (e.g., 30 minutes).

9. Remove tea bags carefully, being careful not to spill any contentsfrom bags, hang from a clip on drip rack for 3 minutes.

10. Carefully remove each bag, weigh, and record (drip weight).

11. Place tea bags onto centrifuge walls, being careful not to let themtouch and careful to balance evenly around wall.

12. Lock down lid and start timer. Spin for 75 seconds.

13. Unlock lid and remove bags. Weigh each bag and record weight(centrifuge weight).

Calculations:

The tea bag material has an absorbency determined as follows:

Free Swell Capacity, factor=5.78

Centrifuge Capacity, factor=0.50

Z=Oven dry SAP wt (g)/Air dry SAP wt (g)

Free Capacity (g/g):

$\frac{\begin{matrix}{\left\lbrack {\left( {{{drip}\mspace{14mu} {wt}\mspace{11mu} (g)} - {{dry}\mspace{14mu} {bag}\mspace{14mu} {wt}\mspace{11mu} (g)}} \right) - \left( {{AD}\mspace{14mu} {SAP}\mspace{14mu} {wt}\mspace{11mu} (g)} \right)} \right\rbrack -} \\\left( {{dry}\mspace{14mu} {bag}\mspace{14mu} {wt}\mspace{11mu} (g)*5.78} \right)\end{matrix}}{\left( {{AD}\mspace{14mu} {SAP}\mspace{14mu} {wt}\mspace{11mu} (g)*Z} \right)}$

Centrifuge Retention Capacity (g/g):

$\frac{\begin{matrix}{\left\lbrack {{{centrifuge}\mspace{14mu} {wt}\mspace{11mu} (g)} - {{dry}\mspace{14mu} {bag}\mspace{14mu} {wt}\mspace{11mu} (g)} - \left( {{AD}\mspace{14mu} {SAP}\mspace{14mu} {wt}\mspace{11mu} (g)} \right)} \right\rbrack -} \\\left( {{dry}\mspace{14mu} {bag}\mspace{14mu} {wt}\mspace{11mu} (g)*0.50} \right)\end{matrix}}{\left( {{AD}\mspace{14mu} {SAP}\mspace{14mu} {wt}*Z} \right)}$

Absorbency Under Load (AUL)

The materials, procedure, and calculations to determine AUL were asfollows.

Test Materials;

Mettler Toledo PB 3002 balance and BALANCE-LINK software or othercompatible balance and software. Software set-up: record weight frombalance every 30 sec (this will be a negative number. Software can placeeach value into EXCEL spreadsheet.

Kontes 90 mm ULTRA-WARE filter set up with fritted glass (coarse) filterplate. clamped to stand; 2 L glass bottle with outlet tube near bottomof bottle; rubber stopper with glass tube through the stopper that fitsthe bottle (air inlet); TYGON tubing; stainless steel rod/plexiglassplunger assembly (71 mm diameter); stainless steel weight with holedrill through to place over plunger (plunger and weight=867 g); VWR 9.0cm filter papers (Qualitative 413 catalog number 28310-048) cut down to80 mm size; double-stick SCOTCH tape; and 0.9% saline.

Test Procedure:

1. Level filter set-up with small level.

2. Adjust filter height or fluid level in bottle so that fritted glassfilter and saline level in bottle are at same height.

3. Make sure that there are no kinks in tubing or air bubbles in tubingor under fritted glass filter plate.

4. Place filter paper into filter and place stainless steel weight ontofilter paper.

5. Wait for 5-10 min while filter paper becomes fully wetted and reachesequilibrium with applied weight.

6. Zero balance.

7. While waiting for filter paper to reach equilibrium prepare plungerwith double stick tape on bottom.

8. Place plunger (with tape) onto separate scale and zero scale.

9. Place plunger into dry test material so that a monolayer of materialis stuck to the bottom by the double stick tape.

10. Weigh the plunger and test material on zeroed scale and recordweight of dry test material (dry material weight 0.15 g±0.05 g).

11. Filter paper should be at equilibrium by now, zero scale.

12. Start balance recording software.

13. Remove weight and place plunger and test material into filterassembly.

14. Place weight onto plunger assembly.

15. Wait for test to complete (30 or 60 min)

16. Stop balance recording software.

Calculations:

A=balance reading (g)*−1(weight of saline absorbed by test material)

B=dry weight of test material (this can be corrected for moisture bymultiplying the AD weight by solids %).

AUL (g/g)=A/B (g 1% saline/1 g test material)

EXAMPLES

The following examples are provided for the purpose of illustrating, notlimiting, the invention. In the following examples a laboratory extruderwas used. It has a cylinder for the material being extruded and a motordriven piston for extruding the material at a controlled rate. Thepiston delivers the material through a spin pack with a spinneret havinga selected diameter. The diameter of the spinneret can be changed. Inthe present examples the spinneret discharged directly into a bath.

Example 1

A solution of CMC 9H4F 10.0 g OD in 450 ml deionized (DI) water wasprepared with vigorous stirring to obtain a CMC solution. Guar gum (0.6g) was dissolved in 25 ml DI water and mix well with the CMC solution.The solution was stirred for one hour to allow complete mixing of thetwo polymers.

The polymer mixture was blended in the blender. Fully dissolve basicdihydroxy aluminum acetate stabilized with boric acid (purchased fromSigma-Aldrich Fine Chemicals) 0.125 g in 25 ml DI water. Transfer thealuminum acetate stabilized with boric acid solution to the polymersolution and blend for five minutes to mix to provide a gel. Leave thegel at ambient temperature (25° C.) for one hour.

Example 2

A solution of CMC 9H4F 10.0 g OD in 950 ml deionized (DI) water wasprepared with vigorous stirring to obtain a CMC solution. Guar gum (0.6g) was dissolved in 25 ml DI water and mix well with the CMC solution.The solution was stirred for one hour to allow complete mixing of thetwo polymers.

The polymer mixture was blended in the blender. Fully dissolve basicdihydroxy aluminum acetate stabilized with boric acid (purchased fromSigma-Aldrich Fine Chemicals) 0.125 g in 25 ml DI water. Transfer thealuminum acetate stabilized with boric acid solution to the polymersolution and blend for five minutes to provide a gel. Leave the gel atambient temperature (25° C.) for one hour.

Example 3

The aqueous gels described above in Examples 1 and 2 were extruded in awet spinning extruder to form a gel fiber. The gel from the Example 1was a 2% by weight solution and the gel from Example 2 a 1% by weightsolution. The get fiber was placed in a denatured ethanol solvent toprecipitate the fibers. There was no second crosslinking. The filamentsformed were 700 μm in diameter. The following table gives the amount ofgel in solution and the free swell, centrifuge capacity and AUL of thefibers. Free swell, centrifuge capacity and AUL are in grams absorbedper gram of fiber.

TABLE 1 gel in centrifuge Example solution, % Free swell capacity AUL 12 31.2 13.32 18.71 1 2 27.16 14.03 22.95 2 1 34.51 17.07 13.23

Example 4

In this example, the preparation of representative mixed polymercomposite fibers crosslinked with fresh aluminum sulfate and freshaluminum sulfate is described. A solution of Weyerhaeuser pine pulp CMC(40 g OD) in 900 ml deionized water was prepared with vigorous stirringto obtain a CMC solution. Guar gum (2.4 g) was dissolved in 50 ml DIwater and mixed with the CMC solution. The solution was stirred for onehour to allow complete mixing of the two polymers.

Weigh 0.8 g of fresh aluminum sulfate octadecahydrate and dissolve in 50ml DI water. Transfer aluminum sulfate solution to the polymer solutionand blend for 5 minutes to mix well. Leave the gel at ambienttemperature (25° C.) for one hour.

The gel was formed into fibers using wet spinning (one orifice with holediameter of 500 micron).

The gel fibers entered a water-miscible solvent bath containing 1200 mlwater and 3600 ml isopropanol containing a second crosslinker. Thecrosslinker concentration in the following table is based on the amountof crosslinker per 4 g dry gel extruded. The second crosslinker was alsofresh aluminum sulfate. Each portion of precipitated fiber was thensoaked in 500 ml of isopropanol and mixed for 10 minutes. The fiberswere then dried.

The following table gives the speed of the gel through the orifice, theamount of crosslinker in the bath, and the free swell, and centrifugecapacity of the composite fiber. Free swell, centrifuge capacity and AULare in grams absorbed per gram of fiber.

TABLE 2 gel rate. centrifuge g/min crosslinker % free swell capacity 300.05 35.4 18.54 30 0.072 41.09 25.16 30 0.084 40.83 26.71 30 0.148 29.313.69 10 0.2 38.79 21.15

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. A method for making mixed polymer composite fibers, comprising: (a)blending a carboxyalkyl cellulose and a galactomannan polymer orglucomannan polymer in water to provide an aqueous solution; (b)treating the aqueous solution with a first crosslinking agent to providea gel; (c) forming gel fibers from the get using melt blowing,centrifugal spinning, wet spinning, or dry-jet wet spinning, (d)treating the gel fibers with a water-miscible solvent to provide mixedpolymer composite fibers.
 2. The method of claim 1 wherein in step (d)the gel fibers are treated in a solvent bath.
 3. The method of claim 1wherein in step (d) the gel fibers are treated by a solvent spray. 4.The method of claim 1 further comprising drying the fiberized fibers toprovide dried crosslinked mixed polymer composite fibers.
 5. The methodof claim 1, wherein the carboxyalkyl cellulose has a degree of carboxylgroup substitution of from about 0.3 to about 2.5.
 6. The method ofclaim 1, wherein the carboxyalkyl cellulose is carboxymethyl cellulose.7. The method of claim 1, wherein the galactomannan polymer is selectedfrom the group consisting of guar gum, locust bean gum, tara gum, andfenugreek gum.
 8. The method of claim 1, wherein the glucomannan polymeris konjac gum.
 9. The method of claim 1, wherein the aqueous solutioncomprises from about 60 to about 99 percent by weight carboxyalkylcellulose based on the total weight of mixed polymer composite fibers.11. The method of claim 1, wherein the aqueous solution comprises fromabout 1 to about 20 percent by weight galactomannan or glucomannanpolymer based on the total weight of mixed polymer composite fibers. 12.The method of claim 1, wherein the first crosslinking agent is acarboxyl group crosslinking agent.
 13. The method of claim 1, whereinthe first crosslinking agent is a hydroxyl group crosslinking agent. 14.The method of claim 1, wherein the first crosslinking agent is selectedfrom the group consisting of aluminum (III) compounds, titanium (IV)compounds, bismuth (III) compounds, boron (III) compounds, and zirconium(IV) compounds.
 15. The method of claim 1, wherein the firstcrosslinking agent is applied in an amount from about 0.1 to about 20percent by weight based on the total weight of mixed polymer compositefibers.
 16. The method of claim 1, wherein the water-miscible solvent isan alcohol.
 17. The method of claim 1, wherein the water-misciblesolvent is selected from the group consisting of methanol, ethanol,isopropanol, and mixtures thereof.
 18. The method of claim 1 furthercomprising treating the gel fibers with a second crosslinking agentduring step (d).
 19. The method of claim 18, wherein the secondcrosslinking agent is selected from the group consisting of aluminum(III) compounds, titanium (IV) compounds, bismuth (III) compounds, boron(III) compounds, and zirconium (IV) compounds.
 20. The method of claim18, wherein the second crosslinking agent is applied in an amount fromabout 0.1 to about 20 percent by weight based on the total weight ofcrosslinked fibers.
 21. A mixed polymer composite fiber, comprising acarboxyalkyl cellulose and a galactomannan polymer or a glucomannanpolymer, having a diameter in the range of 50 μm to 1000 μm.